Pneumatic spring devices

ABSTRACT

A pneumatic spring device includes a cylinder assembly and a piston assembly, so arranged that a compartment is defined within the cylinder, and is filled by a gas, which, under normal conditions, is less dense than nitrogen, preferably helium, and is under high pressure (300 to 1000 bars). When the gas in the compartment is compressed by movement of the piston assembly within the cylinder, a large reserve of energy is thus made available in a small volume, and is maintained, despite variations in temperature. Control means, preferably in the form of an hydraulic jack arrangement, is provided for releasing this energy, and the piston assembly is connected to a device, particularly an electrical circuit breaker for the control thereof.

v United States Patent 1191 Gratzmuller J Aug. 14, 1973 PNEUMATIC SPRING DEVICES [76] Inventor: Jean Louis Gratzmuuer, 66 Pnmary Examiner-James B. Marbert Boulevard Maurice Barres, Attorney-cantor & Kraft Neuilly-sur-Seine, France [22] Filed: Nov. 9, 1971 [57,] ABSTRACT A pneumatic spring device includes a cylinder assem- [21] APPI- 197376 bly and a piston assembly, so arranged that a compartment is definedwithin the cylinder, and is filled by a [30] F l A u fl priority m gas, which, under normal conditions, is less dense than Nov. 13 1970 France 7040607 nitmgen' peferably helium and is high Pmsu (300 to 1000 bars). When the gas in the compartment 52 us. c1. 267/113, 267/65 R by mvemem [511 1111. C1 Fl6f 9/02 a large "Serve energy is thus 58 Field of Search 267/113, 124, 129, a small and is maintained- 267/65 R despite var1at1ons in temperature. Control means, preferably in the form of an hydraulic jack arrangement, is [56] References Cited prosglded for releasing figs energy, andl thle pistclm assem y 1s connecte to a evrce, partlcu ar y an e ectr1- UNITED STATES PATENTS cal circuit breaker for the control thereof. 3,428,303 2/1969 Lynch 267/ 124 3,560,143 2 1971 Sperberg 267 65 R 16 Claims, 11 Drawing Figures PATENTEU AUG 14 I975 SHEET 2 BF 7 Inventor ouis M Jam FIG!

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SHEET '4 [1F 7 PATENTEU AUG 14 I975 BACKGROUND OF THE INVENTION This invention is concerned with improvements in or relating to pneumatic spring devices, i.e. devices in which the spring unit is made up, not of a solid (metal, rubber, etc.,) but by a gas, and it concerns particularly high-power spring devices and, more particularly, devices for equipping circuit-breaker control installations.

It is known that in the many varied mechanical applications, metallic springs are most frequently used, e.g. steel helical springs, whose function is to store energy by deformation.

Pneumatic spring devices are likewise known, substantially comprising a cylinder, a piston, a piston rod and a resilient cushion of air or nitrogen enclosed in the space formed between the piston and one of the ends of the cylinder.

In the majority of applications, and for moderate pressures, steel springs are satisfactory because of their robustness and functional reliability. Such springs make a reserve of energy permanently available, a most important safety factor for certain special applications such as control of circuit-breakers and particularly the release of these devices. Given certain constructive and assembly precautions, breakages of steel springs may be rendered negligible. In view of these advantages of metallic springs, known pneumatic spring devices are relatively seldom used, the more so in that they are more expensive, and in that problems of airtightness of the cushion of gas must be very carefully studied.

However, when the availability of very high forces is required, as for example in the case of rapid release of high-tension circuit-breakers with large cut-out power, metallic springs begin to present certain drawbacks. In fact their weight and bulk becomes excessive, so that their considerable inertia prevents them from releasing in a very short time the energy they have stored. Thus a certain limitation'is set on the power available.

Known pneumatic spring devices, if they were used in the case of high power, would also suffer from certain drawbacks which would not render them preferable to metallic springs.

In fact, in order to limit the bulk and weight of pneumatic spring devices, and thus to limit the inertial of the moving parts, one would be led, in order to have a high degree of power available, to choose high pressures for the resilient cushion of air or nitrogen. But it appears that there is soon a limitation to an increase in pressure in view of the loss of compressibility of the air or nitrogen .in proportion as the pressures increase. In other words, in known pneumatic spring devices, the gas plays its part as a resilient cushion less and less effciently, and tends progressively to behave as a liquid when the pressures increases. Even when rising from 200 to 300 bars (1 bar 0.987 of normal atmosphere about 1.02 kg/cm), the loss of compressibility of the nitrogen is of the order of 20 percent.

It should in fact be noted that Mariottes (or Boyle's) law RV. C" is only a limiting law, which applies only to the perfect gaseous state. As it would be desirable, in order to construct satisfactory high-power pneumatic spring devices, to be able to increase the pressure of the gaseous resilient cushion to pressures above 300 bars and preferably of the order of 400 to 1000 bars, a very considerable deterioration in the resilient qualities of the gas would be reached, necessitating considerable increases in the volume of the gaseous cushion, and, by this fact, losing the very advantages sought after.

Besides, in the case of the high pressures envisaged, temperature variations cause variations in pressure at constant volume which may be very considerable, par-' ticularly if pneumatic spring devices which are fitted to outside installations, (e.g. circuit-breakers) are involved, where the temperatures may vary from 40 to +50C. If it were desired to remedy at least in part these variations originating from temperature fluctuations, control means would have to be provided for the valves, the temperatureregulating means, etc., which would increase costs unacceptably and reduce their functional reliability.

SUMMARY OF THE INVENTION It is an object of the present invention to obviate or mitigate these drawbacks, and enable construction of pneumatic spring devices particularly high-power devices, with qualities superior not only to those of conventional spring devices, but superior to those of metallic springs used until the present time.

BRIEF DESCRIPTION OF THE DRAWINGS According to the present invention there is provided a pneumatic spring device including at least one cylinder assembly and a piston assembly movably mounted in the or each cylinder assembly and defining in the latter at least one variable-volume compartment, the piston assembly including a rod which extends out of at least one end of the cylinder assembly and is provided with means for linking the rod to a device which is to be actuated by the pneumatic spring device, and at least one seal located between a fixed part of the cylinder assembly and a movable part of the piston assembly, said compartment being filled with a gas which,

under normal conditions of temperature and pressure,

has a density less than that of nitrogen, and which is under high pressure.

DESCRIPTION OF THE INVENTION excess of 300 kg per cm of active piston surface .and

for example of the order of 400 to 1000 kg/cm the energy stored in these springs being releasable in a fraction of a second, e.g. from H 10th to one thousandth of a second, depending on the path of the spring, giving a very high specific power.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a sectional view of a first embodiment of a pneumatic spring device according to the invention, wherein the rod is pushed out of the cylinder assembly during operation, devices which operate in this way being hereinafter referred to as being of the pusher yp FIG. 2 is a sectional view of a second embodiment of a pneumatic spring device of the pusher type;

a spring device wherein the rod is retracted into the cylinder assembly during operation, devices which operate in this way being hereinafter referred to as being of the traction type;

FIG. 4 is a sectional view of a fourth embodiment of a spring device wherein the rod extends out of both ends of the cylinder assembly and the device can be operated for pusher or tractional control;

FIGS. 5, 6, and 7 show three further embodiments of pneumatic spring devices incorporating an hydraulic jack arrangement;

FIGS. 8, 9 and 10 are schematic sectional views showing the application of pneumatic spring devices according to the invention to the control of electrical circuit-breakers; and

FIG. 1 l is a group of curves showing the characteristics of a spring device according to the invention filled with helium in comparison to that of a conventional nitrogen spring device.

In the first embodiment shown in FIG. 1, the pneumatic spring device includes a fixed cylinder assembly comprising a cylinder 1 formed of a steel tube, a cylinder base 3 screwed on to one end of cylinder 1, with an interposed sealS, and a cylinder head 7 screwed on to the other end of the cylinder 1.

A piston assembly is movably mounted in the cylinder assembly and comprises a piston rod 9, of constant diameter, which is located in the internal volume 11 of cylinder 1, to operate as a plunger piston.

The passage for rod 9 into the cylinder head 7 is sealed by a packing 13 of the spring type, comprising one or more elastomeric rings kept compressed by a spring 15, with an interposed support ring 17. At its end remote from the ring.l7, the spring is retained by a ring 19 which is compressed between the end of cylinder 1 and a shoulder 21 in head 7. Spring packings of this type are described in French Patent No. l,024,868. Two seals 23 lodged for example in throat portions in ring 19, ensure sealing between cylinder 1 and head 7.

According to this embodiment the spring packing is lodged in a cavity in the fixed part of the apparatus, so that the piston rod 9 needs only minimal machining. There are preferably mounted in the packing a plurality of elastomeric rings 13, with different elastic properties; one at least of these rings may be made of the material marketed under the trade mark TEFLON, as described in French Patents Nos. 1,132,624, 1,297,881 and 1,333,774.

The rod 9 is preferably guided in head 7 at two zones 25, 27, which are relatively short axially, spaced apart, and separated by a machined zone of larger diameter. An elastic scraper ring 29 serves to clean the rod during each movement, and to prevent the penetration of .foreign matter between the rod 9 and the packing 13.

The unit which is to be actuated by the pneumatic spring (e.g. the mobile contact of a circuit-breaker) may be directly or indirectly attached to the outer end of the piston rod 9, which may for this purpose be provided with a thread 31. A stop, such as a ring 32 lodged in a groove 32', prevents the inner end of the piston from passing ring 19.

The internal volume 11 of the cylinder is filled with highly-pressurised helium or another inert gas lighter than nitrogen. Such gases have a loss of compressibility, at the high pressures envisaged, well below that which occurs in known pneumatic spring devices filled with air or nitrogen. Besides, the pressure variations at constant volume due to temperature variations are much less marked than in conventional pneumatic springs.

According to the invention there is chosen for preference as a filler gas for the pneumatic spring device a gas which is a member of the group comprising hydrogen, helium and neon.

Preferably, helium is chosen, as it is incombustible, chemically neutral, does not age, and is easily obtainable.

An inflating valve 33, mounted at any point on the cylinder assembly, e.g. at the centre of the base 3, enables the first filling with helium and if necessary reinflation of the spring should a gas leak occur.

Such an apparatus operates as follows: a part of the cylinder assembly (cylinder 1, the head 7 or the base 3) is fixed to the chassis of the installation, and the outer end of the piston rod 9 is fixed to the mobile unit to be actuated. By sppropriate means, certain of which will be described later, the spring is tensioned, i.e. the mobile unit to be actuated is moved with the piston rod 9 as the latter is inserted, e.g. to level 35, into the cylinder l.v

At this point the pneumatic spring is tensioned, and the mobile unit will always be ready to move over a distance L, when released, under the effect of a force F PXS, P being the helium pressure, e.g. 300 to 1000 bars, and S being the cross-section of the piston rod 9.

An embodiment will be described hereinafter, with reference to FIG. 4, which will illustrate the advantages obtained by a device according to the invention, inflated with helium, compared to a conventional device inflated with nitrogen.

FIG. 2 shows, like FIG. 1, a pneumatic spring device acting as a pusher, but in which the seal packing 13' is supported by the piston rod 9, i.e. the packing 13 is mobile instead of being fixed. The same components have the same reference numbers as in FIG. 1.

The cylinder head 7 is simply screwed on to cylinder 1 to serve as a stop for the piston, but no seal packing is provided between the piston rod 9 and this cylinder head 7 the elastic ring 29 serving only to clean the rod 9.

Piston rod 9 has an annular shoulder 37 on which elastomeric rings of the packing 13' are supported. These rings are kept compressed by a spring 15 which is supported at its other end on a ring 19 which is retained by a clip 39.

The packing 13 is of the same, or spring, type, as in FIG. 1, but it is mobile, and supported by the piston rod 9, i.e. when the piston passes into the cylinder the volume of helium in compartment 11 is defined by base 3, the inner wall of cylinder 1 and the mobile packing 13 (and not by the total inner volume of the cylinder as in FIG. 1).

The embodiment shown in FIG. 3 refers to a heliumfilled pneumatic spring device of the traction type. The end of piston rod 9 carries a mobile spring packing 13, similar to that described with reference to FIG. 2, while cylinder head 7" has a fixed spring packing 41, similar to the packing 13 of FIG. 1, sealing the passage for piston rod 9 through cylinder head 7".

In this embodiment, in which the piston rod 9 operates in traction, the high-pressure helium fills compartment 11' located between piston shoulder 37 (or more accurately packing 13') and cylinder head 7" (or more accuratley packing 41). As a result, inflation valve 33' is no longer mounted on the base 3, but preferably on the cylinder head 7" to communicate with compartment 11".

Naturally, compartment 43,' located between the piston and the base 3, is not filled with pressurised gas and communicates with atmosphere, preferably through a breather valve 45 which prevents impurities from entering the cylinder, but is capable of opening to atmosphere when there is counter-pressure in the variablevolume compartment 43.

The embodiment shown in FIG. 4 concerns a pneumatic spring device with a rod extending out of both ends of the cylinder assembly and capable of acting'as either pusher or puller. Also, the piston is of a differential type.

At the ends of the tube forming the cylinder 1 of the device there is mounted a respective cylinder head 47, 49 which heads are similar to the cylinder heads 7 and 7' in FIGS. 1 and 3, i.e. enclosing a spring packing 51, 53 which is fixed, and which seals the passage of piston rod 55 through the cylinder 1. The piston rod 55 has two sections of different diameters, D and D, and has two stops 57, 59 limiting its travel The unit to be actuated by the spring device may be fixed to end 61 or 63 of the rod 55,depending on whether it is to be controlled as a pusher or as a puller, and the fixed part of the pneumatic spring device is fixed, e.g. by screws 65, on to a fixed frame 61 of the installation.

The internal volume 69 of cylinder 1 is filled with highly-pressurised helium, introduced through the inflation valve 33.

The pressure of the gas is exerted onthe effective surface of the differential piston, i.e. on the difference between the sections of diameter D and D of rod 55.

In FIG. 4, the pressure of the gas tends to push the rod back out of the cylinder 1 through cylinder head 47.

If, in such a pneumatic spring device, the crosssectional areas of the two sections of the rodare 19.63 cm and 12.56 cm respectively, the effective working cross-sectional area of the piston is 7.07 cm*. If the travel of the piston is cm, the volume generated by the piston over its entire travel is: 7.07 X 10 70.7 cm. If it is supposed in this example that the volume of the gas chamber is 1000 cm in the released position of the spring, there will thus be in the tensioned position a gas volume of 1000 70.7 929.3 cm. When the initial inflation pressure (in the relaxed position) is 400 l-tg/cm at a temperature of 30C, and if the spring must be capable of operating between temperature extremes of 35C and +50C (minimum acceptable temperature variations for controls of external electrical circuit-breakers for the average western Europm climate), the test table below gives the pressure variations in kg/cm", in the tensioned and relaxed positions ldepending on whether the spring is inflated with heli ini or nitrogen, at the same initial pressure of 400 kg/c f for C.

Spring relaxed Spring tensioned helium nitrogen helium nitrogen I 330 27s 358 310 m 400 400 435 454 449 471 486 526 scissallfift'ii responds to the tensioned spring, while the as. ("f-2 10 cm abscissa (total travel of the piston) corresponds to the relaxed spring.

The above table indicates for example that, for the helium spring in the tensioned position, at a tempera ture of 35, the pressure is 358 kg/cm. As the effective surface of the piston is 7.07 cm, the force of the spring in these conditions is 358 X 7.07 2,531 kg, as shown at point A in the curves in FIG. 11.

These curves also show that, for extreme conditions, the force of the helium spring according to the invention varies from'2,333 kg (relaxed spring, at 35C, point B on the curve) to 3,436 kg (tensioned spring, at +50C, point C on the curve), or an absolute spread of 1,103 kg, i.e. an increase of 47 percent, while with the same conditions the force of a conventional nitrogen spring would vary from 1,965 kg (point 0) to 3,719 kg (point E), i.e. an absolute spread of 1,754 kg, or an increase of 90 percent.

The advantage gained by the pneumatic spring device according to the invention is therefore considerable, since the variations are reduced roughly to half in comparison to an eventual pneumatic spring. If the spread between the extreme temperatures is greater, which must be expected in some climates, the gain is even greater. 7

For a given temperature, the release curve of the spring, between the tensioned and relaxed positions, could be made equivalent in the cases of helium andnitrogen, on condition that the gas chamber was increased in volume in the case of the nitrogen spring.

In the example considered, the volume of the gas chamber should be increased by 50 percent (from 1000 to 1570 cm), which would thus lead to a heavier, bulkier nitrogen spring, which would thus be more expensive than the helium spring. However, the variation in the force of the spring in the tensioned position would only be corrected by an increase in the volume of the gas chamber.

In installations incorporating pneumatic spring devices according to the invention, means must be provided to tension the springs. In an hydraulic control plant for circuit-breakers, to which the invention applies in particular it is of course advantageous to tension the spring by means of an hydraulic jack arrange-' ment.

FIGS. 5, 6 and 7 show three embodiments, of a pneumatic spring device incorporating an hydraulic jack arrangement for compressing the pneumatic spring. In these three embodiments, the device comprises a cylinder 71 which is common to the pneumatic spring and to the hydraulic jack arrangement. The cylinder 71 is closed at one end by a cylinder base 73, and at the other end by a cylinder head 75 through which there passes in a sealed fashion the piston rod via a fixed spring packing 77.

In the embodiment in FIG. 5, the part of the device serving as a jack is located on the side of cylinder head 75. This jack comprises a piston rod 79, a piston 81 fitted with a seal packing 83, preferably of the spring type, and an element 85 which is an extension of the piston rod. In the head 75 there is provided a highpressure hydraulic-fluid feed-pipe 86 which opens into a compartment 87. A fluid, when introduced under pressure into the compartment 87, is capable of pushing piston 81 (downwards as viewed in FIG. 5) against the pneumatic spring.

The pneumatic spring part of the device is at the end of the cylindr 71 adjacent to the base 73 and comprises a piston 89 fitted with a spring packing 91 and inflation valve 33.

Compartment 93 defined by the piston 89 and the base 73 is filled with high-pressure helium which tends to push piston 89 resiliently upwards, along with the element 85 and the rod 79 at the end of which there is mounted the unit to be controlled, such as the mobile contact of a circuit-breaker. A stop, such as a shoulder 95, limits the outward travel of the rod 79.

The end of elongation 85 is preferably simply supported on piston 89, without being positively attached thereto, in order to avoid any defect arising from misalignment of the two pistons 81 and 89.

In addition to the two compartments 87 and 93 with inversely-variable volumes, the device also comprises an intermediate compartment 90 between the two pistons 81, 89. This intermediate compartment 90, is movable in position relative to the cylinder 71 but is of constant volume, and communicates with atmosphere through an air orifice 96 through which any leakage of oil or helium may escape. In order that the orifice 96 should never open into compartments 87 or 95, the length of elongation 85, which keeps the two pistons apart, must be at least equal to the travel of the piston rod 79.

It will be seen that with such a device it is sufficient to apply and tomaintain the hydraulic pressure through inlet 86 in order to lower and retain in this position the rod 79. However, the helium pneumatic spring constitutes a reserve of energy which is always available for carrying out the inverse movement, i.e. for the return movement of the rod 79 (e.g. for the release of a circuit-breaker).

It will be seen that the device just described, if it seems to fulfil the same functions as a double-action hydraulic jack, ensures much greater reliability because, should the hydraulic installation fail, the resilient energy accumulated in the pneumatic spring is always available.

In the device described with reference to FIG. 5, the piston rod 79 acts as a puller when the hydraulic jack is supplied.

In the device of FIG. 6, the hydraulic jack arrangement and the pneumatic spring are inverted in position, so that the piston rod 79' operates as a pusher when the hydraulic jack is fed. Without repeating the description, it is sufficient to indicate the reference numbers of certain of the units: the piston 89 of the pneumatic spring; the piston 81' of the hydraulic jack; the compartment 93 for helium under pressure and the inlet 86' for hydraulic fluid under pressure.

It should be noted that, in all figures of the drawings,

the devices have been shown in the position corresponding to the relaxed pneumatic spring.

In the embodiments in FIGS. and 6, part of the length of travel of the piston 89, 89' in the cylinder 71 is lost in order to accommodate the intermediate compartment 90 or 90, for communication with the air, between the two pistons.

FIG. 7 shows a device of the same type as that shown in FIG. 6 (piston rod act'mg as a pusher, under the action of the jack), but in which the intermediate compartment 90" in communication with the atmosphere is of very reduced volume. This compartment 90" is located between the two pistons 81" and .89" formed from a single machined part along with the piston rod 79". Both the pistons are thus practically adjacent and the compartment is constituted by a peripheral groove 97 into which there open one or more radial ducts 99, which communicate with an axial channel 101 opening to atmosphere at the free end of rod 79". Any oil or helium leaks may thus be evacuated.

As viewed in FIG. 7, the upper compartment 93" is the compartment filled with helium 'under high pressure, while the lower compartment 87 is the one into which the pressurised hydraulic fluid penetrates through inlet 86". Naturally, the reverse arrangement might be'used in the case of a device in which the piston rod should act as a puller when the hydraulic jack is fed.

FIGS. 8, 9 and 10 show schematically the application of pneumatic springs according to the invention to the control of electrical circuit-breakers.

The circuit-breaker shown in FIG. 8 substantially comprises a cut-out chamber 103 enclosing a fixed contact 105 connected to a voltage input 107, and a movable contact 109 connected electrically by sliding contacts to a voltage output 113.

The cut-out chamber 103 is mounted on an insulating column 115, filled with dielectric, through which passes a connecting insulator rod 117, connected at one end to the movable contact 109, and at the other end to a piston rod 119 of a pneumatic spring device 121.

The device 121 is a helium pneumatic spring device with incorporated hydraulic jack, similar to that described with reference to FIG. 7. As viewed in FIG. 8, the upper compartment 93" of the cylinder is filled with high-pressure helium, and the lower compartment receives the pressurised hydraulic fluid which flows through inlet 86". In order to engage the circuitbreaker and keep it in this state, it is sufficient to admit, and maintain the pressure of, the liquid in compartment 87". In order to release the device, this compartment is voided. The helium pneumatic spring, which thus constitutes a permanently available energy source, thus expands and causes the piston to descend, said piston carrying the movable contact 109 into the released position (in FIG. 8, the piston of the spring with incorporated jack has been shown in simplified form, but it preferably comprises a double piston, as in FIG. 7).

FIG. 9 shows a similar installation for controlling a circuit-breaker in which the dielectric fluid filling the cut-out chamber 103 is a gaseous fluid, e.g. SP6 gas, under slight pressure. In this case the movable contact 109 is advantageously provided with a machined flower channel 123, and carries a piston 125 which slides in a fixed cylinder or jacket 127 whose internal volume is filled with dielectric gas. At the moment of release, piston 125 forces back some dielectric gas which is blown by channel 123 into the are which is established at the moment of cut-ofi between contacts 105 and 109'. In this way the arc is rapidly de-ionised.

The actuation of piston 125, which constitutes a blower pump, needs high power in order that the blowing be effective, implying the use of a high-power spring according to the invention.

FIG. 10 shows a control installation for a multiplechamber circuit-breaker of the type described in French Patent No. 1,334,353.

This installation comprises a helium pneumatic spring device 131, which does not incorporate an hydraulic jack. This pneumatic spring device is of the type described with reference to FIG. 3, i.e. it operates as a puller in order to pull rod 9 upwards on release. The compartment 1 1 is filled with helium, at high pressure, while the upper compartment may communicate with the atmosphere through the breather valve 45.

While the helium pneumatic spring device is located in a partof the circuit-breaker which is live, an hydraulic jack 133 for maintaining the circuit breakers engaged is in contact with earth. The hydraulic jack is fed through a high-pressure oil inlet 135, a piston rod 139 being connected to the mobile equipment of the circuit-breaker by an insulating rod 137 which always acts as a puller.

I claim:

1. pneumatic spring device including at least one cylinder assembly with opposed ends, a piston assembly movably mounted in the or each cylinder assembly, at least one variable-volume compartment defined by the cylinder assembly and the piston assembly, a rod in the piston assembly extending out of at least one of said opposed ends of the cylinder assembly, attachment means provided on the rod for attaching the rod to a device which is to be actuated by the pneumatic spring device, at least one seal located between the cylinder assembly and the piston assembly, and a gas filling said compartment, said gas, under normal conditions of temperature and pressure, having a density less than that of nitrogen, and being under high pressure.

2. A pneumatic spring device according to claim 1, in which the gas is helium.

3. A pneumatic spring device according to claim 1, in which the gas is compressed between 300 and 1000 bars.

4. A pneumatic spring device according to claim 1, including an hydraulic jack arrangement connected with the piston assembly, the cylinder assembly being common to both the piston assembly and the hydraulic jack arrangement.

5. A pneumatic spring device according to claim 1, in which the rod extends out of both of said opposed ends of the cylinder assembly.

6. A pneumatic spring device according to claim 1, in which the or each seal is in the form of a spring packmg.

7. A pneumatic spring device including at least one cylinder assembly with opposed ends, a piston assembly movably mounted in the or each cylinder assembly, at least one variable-volume compartment defined by the cylinder assembly and the piston assembly, a rod in the piston assembly extending out of at least one of said opposed ends'of the cylinder assembly, attachment means provided on the rod for attaching the rod to a device which is to be actuated by the pneumatic spring device, at least one seal located between the cylinder assembly and the piston assembly, and a gas filling said compartment, said gas, under normal conditions of temperature and pressure, having a density less than that of nitrogen, and being under high pressure, the piston assembly comprising a first piston integral with said rod, a first variable-volume compartment defined by said first piston at one of said opposed ends of the cylinder assembly, a second piston connected with said rod, a second compartment defined by said second piston at the other of said opposed ends of the cylinder assembly, one of said first and second compartments being filled with said gas at high pressure, and aperture means in said apparatus defining an inlet communicating with the other compartment for the entry of hydraulic fluid under pressure to said other compartment.

8. A pneumatic spring device according to claim 7, including an element interposed between said first and second pistons to space them apart, said element being of a length at least equal to the length of travel of the pistons, an intermediate compartment defined between said first and second pistons, and orifice means in the cylinder assembly defining a passage extending between said intermediate compartment andthe atmosphere.

9. A pneumatic spring device according to claim 7, in which the rod has opposed ends, and the first and second pistons are adjacent one another at one of said opposed ends of the rod, recess means define an intermediate compartment between the first and second pistons, and an axial bore in the rod forms a channel communicating between said intermediate compartment and the atmosphere.

10. A pneumatic spring device according to claim 7, in which the gas is helium.

11. A pneumatic spring device according to claim 7 in which the gas is compressed between 300 and 1000 bars.

12. A pneumatic spring device according to claim 7, in which the or each seal is in the form of a spring packmg.

13. A pneumatic spring device according to claim 7,

in which the rod extends out of both of said opposed ends of the cylinder assembly.

14. A control installation for an electric circuit breaker, comprising at least one pneumatic spring device including at least one cylinder assembly with opposed ends, a piston assembly movably mounted in the or each cylinder assembly, at least one variable-volume compartment defined by the cylinder assembly and the piston assembly, a rod in the piston assembly extending out of at least one of said opposed ends of the cylinder assembly, attachment means provided on the rod for attaching the rod to a device which is to be actuated by the pneumatic spring device, at least one seal located between the cylinder assembly and the piston assembly, and a gas filling said compartment, said gas, under normal conditions of temperature and pressure, having a density less than that of nitrogen, and being under high pressure.

15. A control installation for an electric circuit breaker, comprising at least one pneumatic spring device, at least one cylinder assembly with opposed ends,

a piston assembly movably mounted in the or each cylinder assembly, at least one variable-volume compartment defined by the cylinder assembly and the piston assembly, a rod in the piston assembly extending out of at least one of said opposed ends of the cylinder asser'nbly, attachment means provided on the rod for attaching the rod to a device which is to be actuated by the pneumatic spring device, at least one seal located between the cylinder assembly and the piston assembly and a gas filling said compartment said gas, under normal conditions of temperature and pressure, having a density less than that of nitrogen, and being under high pressure, the piston assembly comprising a first piston integral with said rod, a first variable-volume compartment defined by said first piston at one of said opposed ends of the cylinder assembly, a second piston connected with said rod, a second compartment defined by breaker according to claim 14, which includes a cylinder-piston arrangement and a dielectric gas provided therein, the circuit breaker having fixed contacts, and the piston of said cylinder-piston arrangement being mechanically connected to said rod of the piston assembly, such that, at the moment the movable contact is released from said fixed contacts, said dielectric gas is blown between the contacts.

I. I! k I! 

1. A pneumatic spring device including at least one cylinder assembly with opposed ends, a piston assembly movably mounted in the or each cylinder assembly, at least one variable-volume compartment defined by the cylinder assembly and the piston assembly, a rod in the piston assembly extending out of at least one of said opposed ends of the cylinder assembly, attachment means provided on the rod for attaching the rod to a device which is to be actuated by the pneumatic spring device, at least one seal located between the cylinder assembly and the piston assembly, and a gas filling said compartment, said gas, under normal conditions of temperature and pressure, having a density less than that of nitrogen, and being under high pressure.
 2. A pneumatic spring device according to claim 1, in which the gas is helium.
 3. A pneumatic spring device according to claim 1, in which the gas is compressed between 300 and 1000 bars.
 4. A pneumatic spring device according to claim 1, including an hydraulic jack arrangement connected with the piston assembly, the cylinder assembly being common to both the piston assembly and the hydraulic jack arrangement.
 5. A pneumatic spring device according to claim 1, in which the rod extends out of both of said opposed ends of the cylinder assembly.
 6. A pneumatic spring device according to claim 1, in which the or each seal is in the form of a spring packing.
 7. A pneumatic spring device including at least one cylinder assembly with opposed ends, a piston assembly movably mounted in the or each cylinder assembly, at least one variable-volume compartment defined by the cylinder assembly and the piston assembly, a rod in the piston assembly extending out of at least one of said opposed ends of the cylinder assembly, attachment means provided on the rod for attaching the rod to a device which is to be actuated by the pneumatic spring device, at least one seal located between the cylinder assembly and the piston assembly, and a gas filling said compartment, said gas, under normal conditions of temperature and pressure, having a density less than that of nitrogen, and being under high pressure, the piston assembly comprising a first piston integral with said rod, a first variable-volume compartment defined by said first piston at one of said opposed ends of the cylinder assembly, a second piston connected with said rod, a second compartment defined by said second piston at the other of said opposed ends of the cylinder assembly, one of said first and second compartMents being filled with said gas at high pressure, and aperture means in said apparatus defining an inlet communicating with the other compartment for the entry of hydraulic fluid under pressure to said other compartment.
 8. A pneumatic spring device according to claim 7, including an element interposed between said first and second pistons to space them apart, said element being of a length at least equal to the length of travel of the pistons, an intermediate compartment defined between said first and second pistons, and orifice means in the cylinder assembly defining a passage extending between said intermediate compartment and the atmosphere.
 9. A pneumatic spring device according to claim 7, in which the rod has opposed ends, and the first and second pistons are adjacent one another at one of said opposed ends of the rod, recess means define an intermediate compartment between the first and second pistons, and an axial bore in the rod forms a channel communicating between said intermediate compartment and the atmosphere.
 10. A pneumatic spring device according to claim 7, in which the gas is helium.
 11. A pneumatic spring device according to claim 7 in which the gas is compressed between 300 and 1000 bars.
 12. A pneumatic spring device according to claim 7, in which the or each seal is in the form of a spring packing.
 13. A pneumatic spring device according to claim 7, in which the rod extends out of both of said opposed ends of the cylinder assembly.
 14. A control installation for an electric circuit breaker, comprising at least one pneumatic spring device including at least one cylinder assembly with opposed ends, a piston assembly movably mounted in the or each cylinder assembly, at least one variable-volume compartment defined by the cylinder assembly and the piston assembly, a rod in the piston assembly extending out of at least one of said opposed ends of the cylinder assembly, attachment means provided on the rod for attaching the rod to a device which is to be actuated by the pneumatic spring device, at least one seal located between the cylinder assembly and the piston assembly, and a gas filling said compartment, said gas, under normal conditions of temperature and pressure, having a density less than that of nitrogen, and being under high pressure.
 15. A control installation for an electric circuit breaker, comprising at least one pneumatic spring device, at least one cylinder assembly with opposed ends, a piston assembly movably mounted in the or each cylinder assembly, at least one variable-volume compartment defined by the cylinder assembly and the piston assembly, a rod in the piston assembly extending out of at least one of said opposed ends of the cylinder assembly, attachment means provided on the rod for attaching the rod to a device which is to be actuated by the pneumatic spring device, at least one seal located between the cylinder assembly and the piston assembly and a gas filling said compartment said gas, under normal conditions of temperature and pressure, having a density less than that of nitrogen, and being under high pressure, the piston assembly comprising a first piston integral with said rod, a first variable-volume compartment defined by said first piston at one of said opposed ends of the cylinder assembly, a second piston connected with said rod, a second compartment defined by said second piston at the other of said opposed ends of the cylinder assembly, one of said first and second compartments being filled with said gas at high pressure, and aperture means in said apparatus defining an inlet communicating with the other compartment for the entry of hydraulic fluid under pressure to said other compartment, and the circuit breaker has a movable contact with which said rod is mechanically connected.
 16. A control installation for an electric circuit breaker according to claim 14, which includes a cylinder-piston arrangement and a dielectric gas provided therein, the circuit breaker having fixed cOntacts, and the piston of said cylinder-piston arrangement being mechanically connected to said rod of the piston assembly, such that, at the moment the movable contact is released from said fixed contacts, said dielectric gas is blown between the contacts. 